1. Field of the Invention
The subject invention pertains to an improved aqueous binding composition for use with fibrous materials. More specifically, the subject invention pertains to the use of a curable binding composition comprising a water-soluble polyamic acid and an organic crosslinking capable of reaction with the polyamic acid. Such polyamic acid is formed by the reaction of a polycarboxylic acid and/or polyanhydride having a molecular weight of at least 150 and ammonia and/or an amine compound. The aqueous binding composition is coated on a fibrous material and is heated to achieve crosslinking to form a water-resistant cured binder in association with the fibrous material wherein adjoining fibers are bound at cross-over points.
2. Description of the Related Art
Binders for fibrous materials, such as fiberglass, have a variety of uses ranging from stiffening applications where the binder is applied to woven or non-woven fiberglass sheet goods and is cured, producing a stiffer product; thermo-forming applications wherein the binder resin is applied to a sheet or lofty fibrous product, following which it is dried and optionally is B-staged to form an intermediate but yet curable product; and to fully cured systems such as building insulation.
Fibrous glass insulation products generally comprise matted glass fibers bonded together by a cured thermoset polymeric material. Molten streams of glass are drawn into fibers of random lengths and are blown into a forming chamber where they are randomly deposited as a mat onto a traveling conveyor. The fibers, while in transit in the forming chamber and while still hot from the drawing operation, are sprayed with an aqueous binder. A phenol-formaldehyde binder has been used throughout the fibrous glass insulation industry. The residual heat from the glass fibers and the flow of air through the fibrous mat during the forming operation are generally sufficient to volatilize water from the binder, thereby leaving the remaining components of the binder on the fibers as a viscous or semi-viscous high solids liquid. The coated fibrous mat is transferred to a curing oven where heated air, for example, is blown through the mat to cure the binder and rigidly bond the glass fibers together.
Fiberglass binders used in the present sense should not be confused with matrix resins which are an entirely different and non-analogous field of art. While sometimes termed “binders”, matrix resins act to fill the entire interstitial space between fibers, resulting in a dense, fiber reinforced product where the matrix must translate the fiber strength properties to the composite, whereas “binder resins” as used herein are not space-filling, but rather coat only the fibers, and particularly the junctions of fibers. Fiberglass binders also cannot be equated with paper or wood product “binders” where the adhesive properties are tailored to the chemical nature of the cellulosic substrates. Many such resins are not suitable for use as fiberglass binders. One skilled in the art of fiberglass binders would not look to cellulosic binders to solve any of the known problems associated with fiberglass binders or binders for use on similar fibrous materials.
Binders useful in fiberglass insulation products generally require a low viscosity in the uncured state, yet possess characteristics so as to form a rigid thermoset polymeric mat for the glass fibers when cured. A low binder viscosity in the uncured state is required to allow the mat to be sized correctly. Also, viscous binders tend to be tacky or sticky and hence they lead to the unwanted accumulation of fiber on the forming chamber walls. This accumulated fiber may later fall onto the mat causing dense areas and product problems. A binder which forms a rigid matrix when cured is required so that a finished fiberglass thermal insulation product or similar product, when compressed for packaging and shipping, will recover somewhat to its as-made vertical dimension when installed in a building.
From among the many thermosetting polymers, numerous candidates for suitable thermosetting fiberglass binder resins exist. However, binder-coated fiberglass products are often of the commodity type, and thus cost becomes a driving factor, generally ruling out in some instances such resins as thermosetting polyurethanes, epoxies, and others. Due to their excellent cost/performance ratio, the resins of choice in the past have been phenol-formaldehyde resins. Phenol-formaldehyde resins can be economically produced, and can be extended with urea prior to use as a binder in many applications. Such urea-extended phenol-formaldehyde binders have been the mainstay of the fiberglass insulation industry for years, for example.
Over the past several decades however, minimization of volatile organic compound emissions (VOCs) both on the part of the industry desiring to provide a cleaner environment, as well as by government regulation, has led to extensive investigations into not only reducing emissions from the current formaldehyde-based binders, but also into candidate replacement binders. For example, subtle changes in the ratios of phenol to formaldehyde in the preparation of the basic phenol-formaldehyde resole resins, changes in catalysts, and addition of different and multiple formaldehyde scavengers, has resulted in considerable improvement in emissions from phenol-formaldehyde binders as compared with the binders previously used. However, with increasingly stringent government regulations, more and more attention has been paid to alternative binder systems which lack formaldehyde.
One such candidate binder system employs polymers of acrylic acid as a first component, and a polyol such as glycerine or a modestly oxyalkylated glycerine as a curing or “crosslinking” component. The preparation and properties of such poly(acrylic acid)-based binders, including information relative to the VOC emissions, and a comparison of binder properties versus urea formaldehyde binders is presented in “Formaldehyde-Free Crosslinking Binders For Non-Wovens”, Charles T. Arkins et al., TAPPI JOURNAL, Vol. 78, No. 11, pages 161-168, November 1995. The binders disclosed by the Arkins article, appear to be B-stageable as well as being able to provide physical properties similar to those of urea-formaldehyde resins.
U.S. Pat. No. 5,340,868 discloses fiberglass insulation products cured with a combination of a polycarboxy polymer, a beta-hydroxyalkylamide, and at least one trifunctional monomeric carboxylic acid, such as citric acid. The specific polycarboxy polymers disclosed are poly(acrylic acid) polymers. See also, U.S. Pat. No. 5,143,582 U.S. Pat. No. 5,318,990 discloses a fibrous glass binder which comprises a polycarboxy polymer, a monomeric trihydric alcohol and a catalyst comprising an alkali metal salt of a phosphorous-containing organic acid.
Published European Patent Application EP 0 583 086 A1 appears to provide details of polyacrylic acid binders whose cure is catalyzed by a phosphorus-containing catalyst system as discussed in the Arkins article previously cited. Higher molecular weight poly(acrylic acids) are stated to provide polymers exhibiting a more complete cure. See also U.S. Pat. Nos. 5,661,213; 5,427,587; 6,136,916; and 6,221,973.
Some polycarboxy polymers have been found useful for making fiberglass insulation products. Problems of clumping or sticking of the glass fibers to the inside of the forming chambers during the processing, as well as providing a final product that exhibits the recovery and rigidity necessary to provide a commercially acceptable fiberglass insulation product, have been overcome. See, for example, U.S. Pat. No. 6,331,350. The thermosetting acrylic resins have been found to be more hydrophilic than the traditional phenolic binders, however. This hydrophilicity can result in fiberglass insulation that is more prone to absorb water, thereby possibly compromising the integrity of the product. Also, the thermosetting acrylic resins now being used as binding agents for fiberglass have been found to not react as effectively with silane coupling agents of the type traditionally used by the industry. The addition of silicone as a hydrophobing agent results in problems when abatement devices are used that are based on incineration. Also, the presence of silicone in the manufacturing process can interfere with the adhesion of certain facing substrates to the finished fiberglass material. Overcoming these problems will help to better utilize polycarboxy polymers in fiberglass binders.
U.S. Pat. No. 6,706,853 discloses a reaction product of a cyclic anhydride and an alkanolamine for use when binding fiberglass. Representative cyclic anhydrides include anhydride polymers of maleic anhydride with styrene and with methacrylate monomers.
It is an object of the invention to provide an improved binding composition for use when binding fibrous materials in the absence of the use of a phenol-formaldehyde binder.
It is an object of the invention to provide an improved process for binding a fibrous material to provide an improved water-resistant cured binder in association with a fibrous material wherein adjoining fibers are bound at cross-over points.
It is a further object of the present invention to provide a bound fibrous material wherein adjoining fibers are bound at cross-over points by means of the cured water-resistant binder of the present invention.
Other objects and advantages of the invention will be apparent to those skilled in the art upon a review of the following description and appended claims.